In the current grant period, these investigators have found that the platypus and echidna, primitive mammals previously thought to lack REM sleep, have REM sleep in very large amounts. This finding suggests that REM sleep may have evolved in the reptilian ancestors of mammals. Aminergic and cholinergic neurons have central roles in REM sleep control. Noradrenergic and serotonergic cells are tonically active during waking and reduce discharge rate in nonREM sleep. During REM sleep, and only during REM sleep, serotonergic and noradrenergic cell groups show a complete cessation of discharge in all mammals examined. A subpopulation of cholinergic cells is selectively active in REM sleep. Other cholinergic cells are active in both waking and REM sleep. Recent immunohistochemical work has established that these three cell groups exist in the reptile. These findings suggest that REM sleep or a precursor state should exist in reptiles. Observation of the discharge patterns of brainstem aminergic and cholinergic cell groups could determine the key neuronal characteristics of reptilian sleep. The investigators propose to conduct the first studies of brainstem monoaminergic and cholinergic cell discharge in non-mammalian species. They will use microwire techniques that allow long term recording in the freely moving animal. They will study the activity of noradrenergic, serotonergic and cholinergic cells during waking and sleep in two reptiles, the box turtle (Terrapene carolina) and the iguana (Iguana iguana). Study of the activity of aminergic and cholinergic cells in reptiles will provide critical data bearing on the evolution of: 1) REM and nonREM sleep states; 2) the waking discharge patterns of aminergic and cholinergic cells; 3) the receptors and membrane mechanisms governing discharge of these cells in mammals; and 3) the functional role of these cell types.